1. Field of the Invention
The present invention relates to a surface acoustic wave device and more particularly, to a surface acoustic wave device in which a sealing resin for sealing a gap between a surface acoustic wave element and a mounting board is prevented from flowing so as to reach a vibrating portion of the surface acoustic wave element.
2. Description of Related Art
One example of a known surface acoustic wave device is disclosed in Patent Document 1 (Japanese Unexamined Patent Application Publication No. 8-316778) and its structure is shown in FIG. 21. In this the surface acoustic wave device 51, a surface acoustic wave element (SAW device chip) 52 and a mounting board 53 are integrated and the functional surface of the surface acoustic wave element 52 is connected to the mounting board 53 through bumps 54.
On the functional surface of the surface acoustic wave element 52, as shown in FIG. 22, a vibrating portion 56 including a comb-shaped electrode portion (hereinafter called an IDT), etc., is provided, a vibration space 57 is secured between the vibrating portion 56 and the mounting board 53, and the outer peripheral edge of the surface acoustic wave element 52 is sealed by using a sealing resin 58 composed of a thermosetting resin such as an epoxy resin, etc. Moreover, on the mounting surface of the mounting board 53, as shown in FIG. 23, electrode lands 59 for connecting the bumps 54 at fixed locations are formed.
Furthermore, in the surface acoustic wave device 51, in order to prevent the sealing resin 58 for sealing a gap between the surface acoustic wave element 52 and the mounting board 53 from flowing to the vibrating portion 56 of the surface acoustic wave element 52, two inner and outer barriers 61 and 62 that block the resin flow, which are made lower than the bumps 54 and disposed so as to enclose the vibrating portion 56, are provided on the functional surface of the surface acoustic wave element 52. That is, the barriers 61 and 62 are formed by using a photoresist and function as a barrier for preventing the sealing resin 56 from flowing in. The reason why these barriers 61 and 62 are set lower than the bumps 51 is that, when the surface acoustic wave element 52 is flip-chip bonded to the mounting board 53, even if the bumps 54 are pressed, the bumps 54 have a sufficient connecting strength and a small gap is secured between the barriers 61 and 62 and the mounting board 53.
In the surface acoustic wave device 51 constructed in this way, the sealing resin 58 coated for sealing the outer peripheral edge of the surface acoustic wave element 52 reaches a gap between the outer barrier 61 and the mounting board 53 due to the surface tension and, according to circumstances, reaches a gap between the inner barrier 62 and the mounting board 53. However, since the gap is narrow, the sealing resin 58 does not flow in over the barriers 61 and 62 and, as a result, the sealing resin 58 is prevented from flowing in so as to reach the vibrating portion 56 of the surface acoustic wave element 52.
However, in the related surface acoustic wave device 51 described above, the relative location of the barriers 61 and 62 and the bumps 54 is not considered and the two barriers 61 and 62 are provided only to enclose the vibrating portion 56. Then, each of the barriers 61 and 62 faces the electrode lands 59 or faces the mounting surface of the mounting board 53 which is exposed, without having the electrode lands 59 formed therebetween. In such a case, the spacing between the barriers 61 and 62 and the mounting surface of the mounting board 53 becomes irregular.
As a result, although the inner and outer barriers 61 and 62 are provided on the functional surface of the surface acoustic wave element 52, the sealing resin 58 cannot be prevented from flowing in over the barriers 61 and 62, and the sealing resin 58 reaches the vibrating portion 56 of the surface acoustic wave element 52 and may attach to the vibrating portion 56. When this occurs, degradation of the performance of the surface acoustic wave device 51 is unavoidable and the rate of defective surface acoustic wave devices 51 increases.